Ovarian Maturation and Spawning of the Deep-Water Mud Shrimp Solenocera Melantho De Man, 1907 (Decapoda, Penaeoidea, Solenoceridae) in Kagoshima Bay, Southern Japan

The deep-water mud shrimp Solenocera melantho is one of the most dominant species in the benthic community of Kagoshima Bay, southern Japan, and is commercially important as the main target species for small-scale trawlers. The reproductive aspects such as ovarian maturation, size at sexual maturity, and spawning season were examined using a large number of female specimens collected from the central area of the bay. This species exhibits an asynchronous type of ovary that contains oocytes of various developmental stages. Ovarian maturity stages were divided into four categories based on the developmental stage of the most advanced oocytes in the ovary: quiescent, developing, early ripe, and ripe. The ripe ovaries contain prematuration-stage oocytes where cortical crypts are found in the peripheral part. Females with ripe ovaries were defined as mature females which would spawn within a few days. The size at sexual maturity of females was estimated to be 25.3 mm in carapace length (1-year old). The gonadosomatic index (GSI = 100 x gonadal weight/body weight) was significantly increased with the progress of ovarian maturation, and most females with GSI 12 were mature. The spawning season was estimated to continue from June to December with its peak during October and November. In the early spawning season, only the 2- and 3-year old groups of females matured. Young females in the 1-year old group matured from July to December.